Sorry for the late reply, but thanks for the advice. I had my younger brother pumping the pedal as I was going around and opening the bleeders. Hopefully, he did not go to the floor with it.
Mushy Brake Pedal After New Brake Lines
- Thread starter Lord Snax
- Start date
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Thanks for the reply. To my knowledge the MC is original. I've never replaced it. Unless the previous owner replaced the MC, than its the original one from the factory. It may be time to replace it. My Mom was driving when the brake lines gave out on a highway with traffic lights on it. She said she sent the pedal to the floor multiple times to get the car to stop. Yup! This is looking more and more like a bad MC.
Just curious, which OBD tool did you use? There aren't many that I am aware of that can bleed ABS, and I've wanted one that can do this for a while.
Could you elaborate what about pushing the pedal to the floor kills the MC? I'm not saying I don't believe you, I just don't follow.
My brakes have been slightly squishy for... well, a long time now, and I've never been able to determine if this has been a tiny amount of air in the system or if it's master cylinder related. But, I think I'm due for a new master cylinder anyway because it looks like it's leaking into the brake booster...
SnowDrifter
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Generally has to do more with a poorly maintained brake system. Accumulated schmoo in the cylinder and/or any corrosion(rough spots) can either embed themselves in the seal, or scrape up the seal enough that the m/c develops an internal leak.
Some times you can have tooling marks or flash that do the same thing when you push the seals to the end of travel. Either way: Same result.
I've always taken quite good care of my braking systems. I don't fear pushing mine to the floor, nor have I ever had an issue with doing so across dozens to hundreds of vehicles (this includes customer vehicle m/c replacements). The way I see it: If bottoming the thing out causes it to go bad, then I'm condemning it anyway and replacing or rebuilding it. I'd rather find out during maintenance in a controlled environment than during say.. A panic stop or a surprise leak in the system - really anything that will cause the thing to depress further than expected.
YMMV
I’m using a Foxwell Scan tool.
Here is the Amazon link: https://www.amazon.com/dp/B072VGJ7S8/ref=cm_sw_r_cp_tai_IvtBCbMW2R6RQ
As for the slightly squishyness you are speaking of. GM SUVs and pickups have always had a slightly squishy brake pedal. As long as you are not sending the pedal to the floor to stop the car, like my brake pedal is doing at the moment, I think you are okay.
The way I understand how working the MC past it’s normal stroke can damage it. Is that when metal parts are made, they are never perfectly smooth, even if they look and feel like they are. There are still microscopic imperfections in the metal. So the rubber seals in the MC, trough normal use, break in to the metal and wear the metal to fit. Over the years the seals can get brittle, and become easier to break. So when you move a very old MC past it’s normal stroke, it puts the old brittle seals on to parts of the MC that we’re never broken in. Resaulting in the destruction of the seals. Hope this helps.
- Lord Snax
@argus Its a little tricky to find the setting that bleeds pump in the Foxwell Scan tool. Here is a video that uses a different scan tool, but it’s very similar. Look around a bit in the abs section and you will find it.
iamdub
Full Access Member
It's wear from age/use and, as Chris @SnowDrifter mentioned, lack of maintenance. The core of the MC is basically a piston in a bore. Over the years of normal braking, this piston is cycled back and forth thousands of times, mostly within a relatively short range of stroke. The piston seal(s) and bore wear together and are "seated/bedded-in" together in this particular area. The rest of the bore is virtually untouched and is still "tight". The difference is extremely small, but the tolerances are tight. Years go by and all is fine until someone pushes the pedal to the floor repeatedly while bleeding the brakes. The aged and fragile seals are then forced into this tighter and even differently-shaped area of the bore and they can be torn, causing loss of pressure. Old, dirty and contaminated fluid (the lack of maintenance Chris mentioned) exacerbates this problem as it's more abrasive from the particulates it contains, so the parts are worn more. There are other factors that determine if flooring the pedal will be an issue or not- The quality of the MC's build when new, the maintenance throughout it's service life, the type of braking primarily performed, etc.
I have also have an issue with the peddle now needing to be pushed further that before I changed my brake lines. I don't recall pushing the peddle further down when the brake line burst in my garage. I had it on jack stands with it running trying to find a slight vibration and when I hit the brakes the line blew. I knew they were getting bad I just couldn't see how bad until it happened and I jacked up the body off the frame to replace them. I have a vacuum bleeder that I use and I have had them bled at a Midas shop and they activated the ABS while doing it. I have read since then that you should have the engine running while bleeding but haven't tried it that way. Would that have any effects on getting all the air out? Maybe it is time to change it out. Seems weird though, the brakes work and I do not have peddle leak down while braking but it used to be at the top of the peddle and now it is close to the bottom. I usually give it 1 pump and the second push feels much better/firmer but it is still much lower than it used to be.
Thoughts???
Thoughts???
iamdub
Full Access Member
Definitely sounds like air. I don't like having the engine running because I can't get an accurate feel for any improvement in the pedal response. If you bleed them and they're better but then get progressively worse, then air is getting into the system somewhere.
My brakes have gotten slightly better over time but no where close to what they were before the brake line replacement. It really sounds like I have air trapped in my MC. I would have thought that even if it did have air in it that all the bleeding I have done and have had done would have got it out.
